The present invention relates broadly to steam turbine power plant control systems, and more particularly to a system which intelligently selects or rejects power plant control modes based on the status of predetermined plant conditions.
Generally, the electrical energy generated from a steam turbine power plant is controlled at a desired power generation level in response to a power generation demand signal modulated by either a power plant operator via an operator's panel or a network dispatcher via an automatic dispatch system (ADS). In accomplishing this control, the power plant may be operated typically in one of a boiler follow mode and a turbine follow mode. Usually, the automatic dispatch system is operated in combination with the controlling turbine follow or boiler follow mode. When the plant control is in the boiler follow mode, the turbine steam admission valves are positioned to admit steam through the steam turbine corresponding to the power generation demand signal and the boiler throttle pressure which is influenced by the steam flow is generally maintained at a desired value by adjusting the boiler firing rate. Similarly, when in the turbine follow mode, the boiler firing rate is controlled to generate steam from the boiler at a rate corresponding to the power generation demand signal and the steam admission valves are positioned to admit steam in response to the boiler firing rate adjustment by maintaining boiler throttle pressure substantially at a desired level.
Previous systems such as that described in U.S. Pat. No. 3,925,645 entitled "System And Method for Transferring Between Boiler-Turbine Plant Control Modes" issued to L. P. Stern on Dec. 9, 1975 and assigned to the same assignee as the present application, have required the plant operator to select the control modes by depressing certain specified push buttons on the operator's panel. This meant that a plant operator would have to be knowledgeable of most of the operational conditions and limitations of the power plant which are sometimes quite subtle and be capable of recognizing those under which the plant may better be controlled in the boiler follow mode and those under which the plant may better be controlled in the turbine follow mode. The plant operator would then take action accordingly. Of course, if certain plant conditions and limitations pass unrecognized, the plant may be operated in a mode which offers undesirable plant protection and/or inefficient plant control which at times may even result in the inability to achieve maximum generated output.
It would be desirable to remove this responsibility from the plant operators and ultimately free them to perform even more supervisory tasks which could result in greater power generation plant availability. By including some known intelligence of plant conditions in the mode selection logic, similar to that of U.S. Pat. No. 3,925,645, it may be possible to acquire an automatic selection of modes which would thereby relieve operator attentiveness in these situations. Such a system is proposed hereinbelow.